private static BuiltinFunction CheckAlwaysNotImplemented(BuiltinFunction xBf) { if (xBf != null) { bool returnsValue = false; foreach (MethodBase mb in xBf.Targets) { if (mb.GetReturnType() != typeof(NotImplementedType) || mb.IsDefined(typeof(Python3WarningAttribute), true)) { returnsValue = true; break; } } if (!returnsValue) { xBf = null; } } return xBf; }